Document processing systems optically and electronically read information from documents, and such information may be stored if not used immediately for processing or subsequently displayed to an operator via a terminal or workstation. Numerous processing systems may lift portions of the image of a document due to the size of the document with respect to the display capability of the terminal such as, for example, a cathode ray tube (CRT).
Present day resolution limits of cathode ray tubes using a 60 Hertz frame refresh rate are approximately 1280 elements in the horizontal direction and 1024 lines in the vertical direction. The CCITT Group III FAX standard for high resolution transmission is 0.005 inches by 0.005 inches. For a document of the size of 8.5 inches by 11 inches cathode ray tube displays require a size of 1728 element by 2200 element. From a comparison of a cathode ray tube resolution and the Group III FAX resolution, it can be seen that an entire standard page cannot be directly, point for point, displayed on a cathode ray tube at a 60 Hertz refresh rate.
The problem of displaying a full image such as one having dimensions 8.5 inches by 11 inches has been addressed by changing the refresh frame rate such as, for example, using a cathode ray tube with a 30 Hertz frame rate. Additionally, a technique for displaying a full page involves the use of thinning the image to display every other element and every other line. The thinning operation results in missing parts of characters which become hard to read.
A need has thus arisen for an image processing system for displaying images of full pages on a standard cathode ray tube. As cathode ray tube resolution improves, so will the requirements for increased FAX resolution and therefore a need will remain for an improved image display method.